Shared Communication Channel Research Articles

Stabilization of linear discrete‐time networked control systems via protocol and controller co‐design

SummaryThis paper investigates the stabilization problem for networked control systems (NCSs) with communication constraint and packet loss. The communication constraint considered is that only one network node is allowed to access a shared communication channel during one time‐slot, and a feedback control is performed with only partially available measurements and control inputs. By taking random packet loss into consideration, a stochastic switched system model is presented to describe the NCS. A sufficient condition is derived for the NCS to be mean‐square exponentially stable, and it is shown that the system performance specified by the exponential decay rate critically depends on the network accessing rates (NARs) of the network nodes and the packet loss probability. The state feedback controller and scheduling protocol, which allocates the NARs, are co‐designed such that the NCS achieves a minimal decay rate. Finally, an illustrative example is given to show the effectiveness of the proposed design approach. Copyright © 2014 John Wiley & Sons, Ltd.

Networked Strong Tracking Filtering with Multiple Packet Dropouts: Algorithms and Applications

This paper focuses on the design problem of a recursive networked strong tracking filter (NSTF) for a class of nonlinear networked systems with parameter perturbations and unknown inputs. The sensors for the networked system are allowed to be spatially distributed in a large geographical area, and signals are transmitted via a shared communication channel with limited capacity. For this kind of system structure, the measurements from different sensors may experience probabilistic data loss with different probabilities. A series of Bernoulli sequences is employed to describe the multiple packet dropout rates. Parameter perturbations and unknown inputs in the system are considered in the filter design process. A recursive networked extended Kalman filter is first derived in the least mean square sense by taking the packet dropout phenomenon into account. Then, a fading factor is introduced in the filter structure in order to cope with the parameter perturbations and unknown system inputs, and a recursive NSTF is derived by developing the so-called networked orthogonal principle. It is shown that the proposed NSTF is capable of providing satisfactory estimation results even in the presence of system parameter perturbations and/or unknown system inputs. A simulation study is carried out on a practical Internet-based three-tank system, and the estimation results show the effectiveness and applicability of the proposed filtering techniques.

Performance of a Wireless Sensor Network MAC Protocol with a Variable Sleep Interval

A MAC protocol specifies how nodes in a sensor network access a shared communication channel. Medium access control protocols for wireless sensor networks are almost always designed to be energy efficient. Desired properties of such MAC protocol are: it should be distributed and contention-free. This study addresses low power MAC protocols utilize energy in efficient manner in wireless sensor networks. We are interested in the trade-off between power consumption and transmission delay, focusing on low traffic in EM-MAC. In EM-MAC, a significant proportion of the nodes may have to stay awake much longer than envisaged. We describe RRMAC protocol (Receiver-Reservation MAC protocol), a new protocol for the Collision avoidance and energy loss due to retransmissions and increase the life span of a wireless sensor networks. This study concludes with the result of simulation studies which indicate that the use of the proposed RRMAC protocol is expected to increase the life time of wireless sensor networks significantly.

Fault detection filter design for stochastic networked control systems

SummaryThis paper is concerned with the fault detection filter (FDF) design for networked control systems subject to time‐varying transmission intervals and delays, packet dropouts, and communication constraints. The considered communication constraint is that only one network node is allowed to gain access to the shared communication channel. Also, the accessing of each node is scheduled by a specified stochastic protocol, and the remote FDFs perform the FD task only with these partially available measurements. By focus on the network‐induced phenomena, the whole FD system are first modeled in the framework of switched stochastic systems with multiple stochastic parameters. Subsequently, by using the multi‐Lyapunov functional approach and novel analysis approach, less conservative conditions including some previous existing results are derived to construct such FDFs. Finally, an example is given to illustrate the effectiveness of the proposed method.Copyright © 2013 John Wiley & Sons, Ltd.

Topological Persistence for Medium Access Control

The primary function of the medium access control (MAC) protocol is managing access to the shared communication channel. From the viewpoint of the transmitters, the MAC protocol determines each transmitter's channel occupancy, the fraction of time that it spends transmitting over the channel. In this paper, we define a set of topological persistences that conform to both network topology and traffic load. We employ these persistences as target occupancies for the MAC layer protocol. A centralized algorithm is developed for calculating topological persistences and its correctness is established. A distributed algorithm and implementation are developed that can operate within scheduled and contention-based MAC protocols. In the distributed algorithm, network resources are allocated through auctions at each receiver in which transmitters participate as bidders to converge on the topological allocation. Very low overhead is achieved by piggybacking auction and bidder communication on existing data packets. The practicality of the distributed algorithm is demonstrated in a wireless network via simulation using the ns-2 network simulator. Simulation results show fast convergence to the topological solution and, once operating with topological persistences, improved performance compared to IEEE 802.11 in delay, throughput, and drop rate.

Implementation and evaluation of scalable vehicle-to-vehicle safety communication control

Vehicle-to-vehicle (V2V) communications play a critical role in enabling numerous important cooperative safety applications. V2V safety communications rely on broadcast of self-state information (e.g., position, speed, and heading) by each vehicle, which allows a vehicle to track its neighboring vehicles in real time. One of the most pressing challenges in this research is to maintain acceptable tracking accuracy of neighboring vehicles while avoiding congestion in the shared communication channel. In this article we describe the evaluation of a transmission control protocol that adapts the message rate and transmission power for V2V safety communications. This protocol has been implemented on V2V test vehicles with wireless radios and integrated with existing active safety applications. The testing and evaluation results show that proposed communication design works well in practice, its performance matches the observations from previous simulations and shows great promise for a large-scale deployment of V2V cooperative safety systems.

Adaptive filtering with bandwidth constraints in the feedback path

This paper introduces a new, adaptive-filter-based controller that shows advantageous properties from the viewpoint of its communication requirement. The algorithm is called signed-error filtered-x LMS (SE-FxLMS). Its novelty is characterized by the fact that it makes possible data compression in the feedback path of adaptive-filter-based control loops in a very simple way. This feature is especially useful in such closed-loop systems where the feedback signals are transmitted over a low-bandwidth communication channel. This is a typical case in so-called networked control systems (NCS), where the communication is carried out over a shared communication channel, e.g., using a wireless sensor network. The paper introduces an analysis of the algorithm as well.

Optimal linear estimation for networked systems with communication constraints

This paper is concerned with the optimal linear estimation problem for discrete time-varying networked systems with communication constraints. The communication constraint considered is that only one network node is allowed to gain access to a shared communication channel, then the various network nodes of the networked systems are scheduled to transmit data according to a specified media access control protocol, and a remote estimator performs the estimation task with only partially available measurements. The channel accessing processes of those network nodes are modeled by Bernoulli processes, and optimal linear filters are designed by using the orthogonal projection principle and the innovation analysis approach. It is shown that the optimal estimation performances critically depend on the channel accessing probabilities of the network nodes and the packet loss probability, and the optimal filters can be obtained by solving recursive Lyapunov and Riccati equations. An illustrative example is finally given to show the effectiveness of the proposed filters.

CONTENTION RESOLUTION IN MULTIPLE-ACCESS CHANNELS: k-SELECTION IN RADIO NETWORKS

In this paper, contention resolution among k contenders on a multiple-access channel is explored. The problem studied has been modeled as a k-Selection in Radio Networks, in which every contender has to have exclusive access at least once to a shared communication channel. The randomized adaptive protocol presented shows that, for a probability of error 2ε, all the contenders get access to the channel in time (e+1+ξ)k + O( log 2(1/ε)), where ε ≤ 1/(n+1), ξ > 0 is any constant arbitrarily close to 0, and n is the total number of potential contenders. The above time complexity is asymptotically optimal for any significant ε. The protocol works even if the number of contenders k is unknown and collisions cannot be detected.

Tag anti-collision algorithms in RFID systems

RFID is a wireless communication technology that provides automatic identification or tracking and data collection from any tagged object. Due to the shared communication channel between the reader...

Contention-free MAC protocols for asynchronous wireless sensor networks

A MAC protocol specifies how nodes in a sensor network access a shared communication channel. Desired properties of a MAC protocol are: it should be contention-free (avoid collisions); it should be distributed and self-stabilize to topological changes in the network; topological changes should be contained, namely, affect only the nodes in the vicinity of the change; it should not assume that nodes have a global time reference, that is, nodes may not be time-synchronized. We give a set of TDMA-based MAC protocols for asynchronous wireless sensor networks satisfying all of these requirements. The communication complexity, number and size of messages, for the protocols to stabilize is small, poly-logarithmic in the network size.

On the feedback information in stabilization over unreliable channels

We consider the remote stabilization of linear systems using shared communication channels where transmitted messages may randomly be lost. We extend the results on the limitations arising in such systems and study the case where there is no feedback information from the actuator side to the controller side. The proposed control scheme utilizes a protocol shared by the actuator and the controller to carry out state and input estimation.

Multiaccess Quantum Channels

Shared communication channels are subject to multiple-access interference. Transmitter and receiver design techniques that explicitly deal with this interference have been shown to improve substantially the performance of communication systems over radio-frequency and other "classical" channels. Quantum multiple-access communication channels, on the other hand, have received comparatively little attention. In this paper, an input-output model for multiple-access quantum channels relevant to optical communications is proposed. The model accounts for multiaccess interference, signal attenuation, and random noise, and can be used in the analysis and design of communication systems. Using a result from optimization, a perturbation method is developed to find the minimum achievable error probability in small-interference channels. It is shown that the quantum measurement that minimizes the error probability in a no-interference channel is robust in the presence of small multiaccess interference. The results are illustrated with numerical examples, which show that optimal quantum detectors can significantly outperform conventional detectors even for moderate levels of crosstalk.

System-level performance analysis for designing on-chip communication architectures

This paper presents a novel system-level performance analysis technique to support the design of custom communication architectures for system-on-chip integrated circuits. Our technique fills a gap in existing techniques for system-level performance analysis, which are either too slow to use in an iterative communication architecture design framework (e.g., simulation of the complete system) or are not accurate enough to drive the design of the communication architecture (e.g., techniques that perform a "static" analysis of the system performance). Our technique is based on a hybrid trace-based performance-analysis methodology in which an initial cosimulation of the system is performed with the communication described in an abstract manner (e.g., as events or abstract data transfers). An abstract set of traces are extracted from the initial cosimulation containing necessary and sufficient information about the computations and communications of the system components. The system designer then specifies a communication architecture by: 1) selecting a topology consisting of dedicated as well as shared communication channels (shared buses) interconnected by bridges; 2) mapping the abstract communications to paths in the communication architecture; and 3) customizing the protocol used for each channel. The traces extracted in the initial step are represented as a communication analysis graph (CAG) and an analysis of the CAG provides an estimate of the system performance as well as various statistics about the components and their communication. Experimental results indicate that our performance-analysis technique achieves accuracy comparable to complete system simulation (an average error of 1.88%) while being over two orders of magnitude faster.

Understanding how Train Dispatchers Manage and Control Trains: A Cognitive Task Analysis of a Distributed Team Planning Task

A Cognitive Task Analysis was conducted to examine how experienced train dispatchers manage track use. The results reveal the cognitive complexities faced by dispatchers and the cognitive and collaborative strategies developed in response to those demands, including strategies to support anticipation and planning, and proactive strategies to exploit windows of opportunity to satisfy the multiple demands on track use. In many cases these strategies depend on communication and cooperation among individuals distributed across time and space (i.e., multiple dispatchers, engineers, maintenance of way personnel). The ability to “listen in” on communications directed at others that have a bearing on achievement of your own goals and to recognize when information in your possession is of relevance to others, are important contributors to safe and efficient track use. The results reinforce findings from other domains (e.g., space shuttle mission control, air traffic control) regarding the role of a shared communication channel in supporting anticipation and contingency planning. Implication for the introduction of advanced “data-link” communication technologies, as well as for dispatcher training are discussed.

Lossless aggregation: a scheme for transmitting multiple stored VBR video streams over a shared communications channel without loss of image quality

This paper introduces a new concept called lossless aggregation for the transmission of video information. It is a scheme for the delivery of variable bit-rate (VBR) video streams from a video server to a group of users over a shared channel. No data are dropped at the source during the adaptation process that reshapes the VBR video traffic to conform to the channel bit-rate characteristics. The transmission schedules of individual video streams evolve in a dynamic way that depends on their relative traffic characteristics. Receiver buffer underflow and overflow are prevented. Therefore, the data delivery process does not cause any loss of image quality. We show that very significant receiver-buffer reduction can be achieved with aggregation compared with the independent transmission of individual video streams over separate channels. Several bandwidth allocation methods for aggregation are studied extensively. The frame equalization algorithm stands out in terms of its simplicity and optimality.

Dynamic prioritized conflict resolution on multiple access broadcast networks

In a multiple access broadcast network, all network nodes share a single shared communication channel, and there is the possibility of a collision when two or more nodes transmit at overlapping times. We propose a dynamic prioritized conflict resolution algorithm in which, when a collision occurs, all colliding messages are retransmitted according to their priority. When a new message arrives, it is allowed to participate in the algorithm as soon as it finds its priority is higher than that of some broadcast message. Using a time-slotted model, for any arrival pattern and priority distribution, we show that our algorithm runs in expected linear time, i.e., O(r), where r is the total number of message transmitted. We also show that the expected waiting time for any message x is O(rank(x)+log s), where rank(x) is the expected number of messages with higher priority which transmit while x is waiting, and s is the minimum of the total number of messages participating in the algorithm and the total number of nodes in the network. The analysis presented in this work also includes an improved analysis of our original (static) prioritized conflict resolution algorithm. This work is applicable to multimedia communications where different priority values could be assigned to different kinds of traffic, and our algorithm ensures that the high-priority real-time traffic has the minimum delay.

Collision avoidance tree networks

Abstract The Collision Avoidance Tree is a local area network based on a hardware device called the collision avoidance switch. The collision avoidance switch arbitrates random access to a shared communication channel and avoids the penalty of collisions among packets. This network combines the benefits of random access (low delay when traffic is light; simple, distributed, and robust protocols) with concurrency of transmission, excellent network utilization and suitability for the domain of high-speed optical networking. The Collision Avoidance Tree is classified in two groups: the Collision Avoidance Single Broadcast (CASB) Tree and the Collision Avoidance Multiple Broadcast (CAMB) Tree. The CASB Tree allows only a single transmission on the network at a given time, while the CAMB Tree allows concurrent transmissions on the network. This paper describes network architectures (station and switch protocols) as well as designs and implementations. Performance results derived from analyses, simulations, and measurements of experimental networks are also presented.

Optimal prioritized conflict resolution on a multiple access channel

A multiple access broadcast network (MABN) is a computer network in which there is a single shared communication channel and every network node can receive all messages transmitted over the channel. A major difficulty in using broadcast communication is the issue of access to the channel. The authors deal with the following prioritized conflict resolution problem: a collection of c messages is initially distributed among nodes on an MABN; each message is associated with a value representing its priority or deadline; and it is required that the messages be broadcast in ascending order of this value. This problem is solved by a distributed prioritized conflict resolution algorithm. It is proved that the expected waiting time of the ith network node to transmit is Theta (i+log c), which is optimal. It is also shown that the algorithm runs in the expected linear time, which is optimal in both the number of slots used and the total elapsed time including local processing.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Space-Time Models of Asynchronous CSMA Protocols for Local Area Networks

Carrier sense multiple-access (CSMA) protocols are widely used in local area networks (LAN's) to control access to a shared communications channel such as a coaxial cable or radio frequency band. CSMA protocols are designed to exploit the property that the signal propagation time across the LAN is much smaller than the packet transmission time. Consequently, their performance depends on the exact timing of a sequence of asynchronous events originating at different points in the network. Previous models of CSMA protocols have not captured this essential space-time characteristic. Instead, the system has been reduced to a 1-dimensional model (i.e., a sequence of events on a single time line) by assuming either that events are synchronous (i.e., slotted operation of the protocol) or that all stations are mutually equidistant (so it can be assumed that each station's time line is identical). The novelty in our work is to describe the system state in terms of an ( N + 1 )-dimensional of space-time, allowing us to faithfully model the exact timings of events for LAN's where the stations are distributed over a fully connected region in N -space. For example, an Ethernet-like network can be viewed as a 1-dimensional LAN, a terrestrial packet radio network can be viewed as a 2dimensional LAN, and so on. First we highlight some of the key properties exhibited by such a model in the general case, including the notion of an embedded Markovian sequence of idle points, and the decomposition of the space-time ribbon into cycles (each of which can be further decomposed into a number of regions). Then we present extensive results for the interesting special case of a 1-dimensional LAN, i.e., an Ethernet-like network. Our results show that previous models of bus LAN's can significantly underestimate their performance.